1. Field of the Invention
The invention relates generally to seismic shear wave sources and, more particularly, but not by way of limitation, it relates to an improved shear wave vibrator for omni-directional coupling of shear wave energy through a telescoping tube into an earth medium.
2. Description of the Prior Art
The prior art includes a number of different types of shear wave vibrator that utilize various structures for coupling shear wave energy into an earth medium. Primarily, prior art apparatus has utilized varying forms of base plate and cleat or blade structure for maintaining positive earth engagement. Still other vibrator structures are known that utilize a cup-like structure for energy engagement in soft earth areas, e.g., U.S. Pat. No. 3,365,019 entitled "Seismic Vibrator For Marshland and Submarine Use".
The earlier types of earth-coupling mechanism have been associated with various forms of shear wave vibrator or the well-known compressional wave vibrator, and Applicant knows of no prior teachings directed to omni-directional continuous coupling of shear waves, e.g., elliptically polarized shear waves. Applicant is aware of a recently developed impulsive source that is capable of generating shear waves in any direction while simultaneously generating compressional waves, but this is primarily no more than a rotatable directional source. There is yet another recent development in the form of a shear wave vibrator having a rotatable base that enables selective generation of S.sub.H or S.sub.v shear waves.